sea-streamer-socket: Backend-agnostic Socket API

Akin to how SeaORM allows you to build applications for different databases, SeaStreamer allows you to build stream processors for different streaming servers.

While the sea-streamer-types crate provides a nice trait-based abstraction, this crates provides a concrete-type API, so that your program can stream from/to any SeaStreamer backend selected by the user on runtime.

This allows you to do neat things, like generating data locally and then stream them to Redis / Kafka. Or in the other way, sink data from server to work on them locally. All without recompiling the stream processor.

If you only ever work with one backend, feel free to depend on sea-streamer-redis / sea-streamer-kafka directly.

A small number of cli programs are provided for demonstration. Let's set them up first:

```shell

The clock program generate messages in the form of { "tick": N }

alias clock='cargo run --package sea-streamer-stdio --features=executables --bin clock'

The relay program redirect messages from input to output

alias relay='cargo run --package sea-streamer-socket --features=executables,backend-kafka,backend-redis --bin relay' ```

Here is how to stream from Stdio ➡️ Redis / Kafka. We generate messages using clock and then pipe it to relay, which then streams to Redis / Kafka:

```shell

Stdio -> Redis

clock -- --stream clock --interval 1s | \ relay -- --input stdio:///clock --output redis://localhost:6379/clock

Stdio -> Kafka

clock -- --stream clock --interval 1s | \ relay -- --input stdio:///clock --output kafka://localhost:9092/clock ```

Here is how to stream between Redis ↔️ Kafka:

```shell

Redis -> Kafka

relay -- --input redis://localhost:6379/clock --output kafka://localhost:9092/clock

Kafka -> Redis

relay -- --input kafka://localhost:9092/clock --output redis://localhost:6379/clock ```

Here is how to replay the stream from Kafka / Redis:

shell relay -- --input redis://localhost:6379/clock --output stdio:///clock --offset start relay -- --input kafka://localhost:9092/clock --output stdio:///clock --offset start